U.S. Pat. No. 3,960,998 by the same inventor relates to a method of producing large rigid foam panels in which a flexible ribbon is coated on one side with plastic foam and immediately thereafter laid on a form with the foam coated side disposed against the form. A number of lengths are laid side-by-side on the form with the edges flowing and cohering together to provide a panel having the shape of the form. An object of this invention is to provide a method and apparatus for making foam plastic boardstock either per se or adhered to another surface, such as a backing sheet or a flat roof.